1. Field of the Invention
The present invention relates to stabilizer for creping adhesives and more Particularly it relates to a creping composition comprising water soluble polymer and stabilizer comprising certain acids or salts thereof.
2. Description of the Prior Art
The creping process is commonly practiced in the manufacture of tissue and towel grades of paper. This process involves scraping the dried paper web from a drying cylinder (Yankee dryer) by the use of a creping doctor blade. The creping action imparts a fine, rippled texture to the sheet and also increases the bulk of the sheet, resulting in improved softness and absorbency. An adhesive formulation is often used to control the adherence of the paper sheet to the Yankee dryer. In this regard, fibrous webs, particularly paper webs, are conventionally subjected to the creping process in order to give them desirable textural characteristics, such as softness and bulk. The creping process typically involves applying creping adhesive--generally in the form of an aqueous solution, emulsion or dispersion--to a drying surface for the web; preferably, this surface is the surface of a rotating creping cylinder, such as the apparatus known as a Yankee dryer. The web is then adhered to the indicated surface. It is subsequently dislodged from the surface with a creping device--preferably, a doctor blade. The impact of the web against the creping device ruptures some of the fiber-to-fiber bonds within the web, causing the web to wrinkle or pucker. The creping adhesive solution, emulsion or dispersion can be comprised of one or more adhesive components, typically water-soluble polymers, and may also contain one or more release agent components as well as other desired additives that may affect the creping process. This is known as the creping adhesive package. This adhesive is exposed to high temperatures (on the ordeir of 100.degree. C.) and high mechanical shear at the creping blade. Given these conditions, one could expect the adhesive formulation to undergo thermooxidative degradation in the presence of atmospheric oxygen. In fact, dark gummy deposits are sometimes observed on the creping blade or Yankee dryer. these deposits are probably thermooxidative degradation products of the creping adhesive formulation and can cause disruptions in the papermaking process. The present invention describes additives for the creping adhesive formulation that significantly reduce the degradation of the creping adhesive formulation under its expected use conditions.
Espy & Maslanka, U.S. Pat. No. 5,338,807 and Espy & Giles, Canadian Patent 979,579 disclose polyamidoamine-epichlorohydrin resins (PAE resins) as adhesives in the creping process for producing tissue and towel paper products.
A number of patents disclose the use of hypophosphorous acid and its salts as antioxidant in polymeric formulations. These include Papero, U.S. Pat. No. 3,242,134 closing use as a stabilizer for polyamides, Yoshitomi, Nagakura and Matsunuma, Japanese Patent 12,997 disclosing use as an antioxidant in the preparation of alkyd resins, Schuler, Swiss Patent 326,175 disclosing use as a light stabilizer for poly(vinyl chloride) and French Patent 1,391,335 (Imperial Chemical Industries Ltd.) disclosing use as a stabilizer in the preparation of polyurethane foams.
The polymers described in the prior art as stabilized by hypophosphorous acid and its salts are all water-insoluble materials. There is no indication given in the prior art that these stabilizers would work in an aqueous system with a water-soluble polymer.
Chen U.S. Pat. No. 4,883,564 discloses a ci-eping adhesive comprising water-soluble binder (polyvinyl alcohol) and a phosphate salt in order to reduce the hard film build up on the creping surface of the drum dryer.
There is no disclosure in the above references of additives used to impart thermal stability to the creping adhesive compositions.
There is no mention in the above references of oxidative instability neither of polyamidoamine-epichlorohydrin or polyamine-epichlorohydrin resins nor of the use of hypophosphorous acid and its salts as stabilizers for polyamidoamine-epichlorohydrin or polyamine-epichlorohydrin creping adhesives.